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I ride a 5 year old commuter bike with a Shimano Nexus 8 internal hub gear, that's done about 20,000km.

I'm not sure if I'm imagining it, but it seems like my bike has lost a considerable amount of mechanical efficiency recently. I now seem to be the slowest bike on the road; everybody passes me and I never overtake anyone, despite keeping the types pumped and the chain lubed. I don't ride any other bike, so it's hard to benchmark, but it feels like the hub slips a little inside as it operates, compared to the feel of a derailleur.

Engagement and changes is still 100% reliable in all 8 gears however.

Is this a known problem with ageing hub gears? Has anyone had this kind of experience before?

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3  
If the hub is becoming less efficient it will get hot. If energy is being lost it must go somewhere, and that somewhere is heat. –  Daniel R Hicks Sep 3 '12 at 0:24
    
Have you had your hub repacked with grease at any point in the last 5 years? –  Rider_X Sep 3 '12 at 19:31
    
@Rider_X I had the hub repacked with grease once, at about the 4 yr mark. –  Ben Hutchison Mar 21 at 5:32
    
@DanielRHicks Yes, that's a good point. Feeling the hub, there is no perceptible hotness in it at the end of my commute. –  Ben Hutchison Mar 21 at 5:34

2 Answers 2

If it is 5 years old and you have been going 20k kilometers I think it would be fair to buy a new one.

The hub can not loose efficiency, but the bearings can become sluggish, also the bearings in the wheels would be a good idea to check.

I have a racingbike and i change my chain every year and whenever i feel the bearings is slower I also change them, and that way more often that every 5 year.

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I am sorry but 20k is not too much to expect from a properly maintained hub. Also you should change the chain by the amount of stretch, which may or may not fall on a yearly schedule. I typically change the chain on my race bike 3-4 times a year, or approximately 2000 km, depending on conditions (rain, dust , etc). Finally, I hate to be pedantic, but chains have bushings, not bearings. –  Rider_X Sep 3 '12 at 19:28
    
Try reading it again, you obvious did not get what i wrote about the bearings. And if you has that much money to change your chain 3-4 times a year, you should do that, but that is not normal. –  Kevin Simper Sep 4 '12 at 6:35
    
You are correct in that I misread what you wrote about bearings, my bad. But you honestly should be change the chain by wear (which could be once very year or 2-4 times a year depending on your mileage and conditions). The 3-4 times I quoted was under heavy mileage and was cheaper than replacing a whole drive train, which would be required if I simply ran one chain that year. A stretched chain changes the pitch of the gears making them incompatible with a new chain. –  Rider_X Sep 4 '12 at 14:38
    
Hehe, I know the problem about incompatible with a new chain. Therefore i do not change it that much :) I drive 12000 kilometers a year on that bike. –  Kevin Simper Sep 5 '12 at 7:34

In the 5 years have you had the hub rebuilt / repacked with grease? The maintenance schedule for the Nexus 8 speed is every 5000 km or 2 years, which ever comes first (I believe). If you have not had any maintenance in your 5 years this is likely the culprit for decreased performance.

20,000 km should be no problem for a properly maintained hub; however, if you have gone without maintenance there is a chance you have started damaging the internals though intrusion of dirt and water. I would hesitate to speculate what may be going wrong (perhaps the roller clutch), but there are quite a few parts that all require proper lubrication.

Either way, I would take it to a certified Shimano dealer to have a look over. They can tell you if the hub is still viable hub, and if so, what maintenance needs to be done.

If you are interested to learn more about the internal workings of your nexus hub, may I suggest starting here.

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